DNA markers will be derived from a mouse telomeric yeast artificial- chromosome (MTY) library and used for telomeric closure of physical and genetic linkage maps of mouse chromosomes. The mouse has been and will likely continue to be the principal mammalian model organism for studying human diseases, and a complete, high-resolution map of the mouse genome will contribute to the further development of the mouse as an experimental organism by facilitating the positional cloning of genetically mapped loci. Physically defined, telomeric markers for individual mouse chromosome ends are essential for such a map. A telomeric YAC cloning system used successfully for isolating human telomeric DNA will be modified and streamlined to allow the efficient isolation of mouse telomeric DNA from Mus spretus. Large-DNA probes corresponding to the centromeric end of insert sequences cloned in the telomeric YACs will be obtained by two methods: (1) by screening a mouse genomic P1 library with vector-insert junction sequence-tagged sites (STSs) derived from the YACs, and (2) by cloning insert DNA directly from the mouse telomeric YACs using a bacterial artificial-chromosome (BAC) vector and marker-rescue methods. These probes (70 - 200 kb in size) will be mapped cytogenetically using fluorescent in situ hybridization methods and then screened for the presence of highly polymorphic DNA markers. The polymorphic markers will be used to map the cloned telomeric DNA genetically relative to current mouse linkage maps. The cytogenetic probes will define the physical ends of individual mouse chromosomes, and will be very useful for a wide range of cytogenetic mapping experiments (including the analysis of cryptic telomeric translocations and analyses of large-scale telomeric polymorphisms amongst mouse species and subspecies). The STSs derived from both the linkage markers themselves and the vector-insert junction regions of the YACs will constitute PCR-based DNA markers for the 10 to 14 Mb of cloned telomeric mouse DNA potentially represented in the MTY library; as such they will help provide telomeric closure for mouse physical and genetic linkage maps and will represent a unique source of precisely mapped probes for the future delineation of global synteny patterns between mouse and human genomes.